fix: force public npm registry for pnpm self-installer bootstrap

pnpm/action-setup bootstraps itself via npm before pnpm is available.
If a repo has a custom registry in .npmrc (e.g. pointing to JFrog or
Nexus), the self-installer tries to fetch pnpm from that registry
without credentials and fails with exit code 1.

Setting NPM_CONFIG_REGISTRY overrides .npmrc for this step only,
ensuring pnpm is always fetched from the public registry. Private
registry auth is configured in subsequent steps once pnpm is ready.

pnpm-build/action.yml

@@ -50,6 +50,12 @@ runs:
       # pnpm/action-setup v4.3.0 — https://code.forgejo.org/pnpm/action-setup/commits/tag/v4.3.0
       - name: Install pnpm
         uses: pnpm/action-setup@b906affcce14559ad1aafd4ab0e942779e9f58b1
+        env:
+          # Override any registry configured in .npmrc (e.g. JFrog or Nexus).
+          # pnpm/action-setup bootstraps itself via npm before pnpm is available,
+          # so it must reach the public npm registry. Auth for private registries
+          # is configured in a later step, after pnpm is installed.
+          NPM_CONFIG_REGISTRY: https://registry.npmjs.org
         with:
           version: ${{ inputs.pnpm-version }}